The flat-panel display devices that are widely used at present are active-matrix liquid crystal display devices using thin-film transistors (TFTs) (hereinafter, referred to as “TFT-LCD devices”).
The liquid crystal panel of the TFT-LCD device includes a pair of opposing substrates (hereinafter referred to as “first and second substrates”). These substrates are fixed at a predetermined distance from each other, and a liquid crystal material is filled in between the substrates to form a liquid crystal layer. At least one of the substrates is transparent; in order to effect a transmissive display, the substrates are both required to be transparent. The TFT-LCD device has a plurality of parallel scanning signal lines provided on the first substrate, and a plurality of data signal lines provided perpendicular to the scanning signal lines. Provided at each intersection between the scanning signal lines and the data signal lines are a pixel electrode, and a pixel TFT, which is a switching element for electrically connecting the pixel electrode to the data signal line. The pixel TFT has a gate terminal connected to the scanning signal line, a source terminal connected to the data signal line, and a drain terminal connected to the pixel electrode.
A common electrode is provided as a counter electrode over the entirety of the second substrate being opposed to the first substrate, and liquid crystal capacitances are formed by the pixel electrodes on the first substrate, the common electrode on the second substrate, and liquid crystal sandwiched therebetween. In addition, auxiliary capacitance lines are provided on the first substrate so as to cross the pixel electrodes, and auxiliary capacitances are formed by the pixel electrodes and the auxiliary capacitance lines.
A data signal line driver circuit, a scanning signal line driver circuit, a common electrode driver circuit, and an auxiliary capacitance line driver circuit are provided in order to respectively drive the data signal lines, the scanning signal lines, the common electrode, and the auxiliary capacitance lines. In addition, the data signal line driver circuit and the scanning signal line driver circuit apply a voltage to each pixel electrode in accordance with an image to be displayed, and a common electrode driver portion and an auxiliary capacitance line driver portion respectively apply an appropriate voltage to the common electrode and the auxiliary capacitance lines. As a result, the voltage that corresponds to the value of each pixel for the image to be displayed is held by the liquid crystal capacitance and the auxiliary capacitance, which are formed by the pixel electrode associated with that pixel, and the voltage that corresponds to the difference in potential between the pixel electrode and the common electrode is applied to the liquid crystal layer.
The applied voltage makes it possible to control the optical transmittance of the liquid crystal layer, and thereby to display the image in accordance with the voltage supplied to each pixel electrode.    [Patent Document 1] Japanese Laid-Open Patent. Publication No. 8-248389